Self-aligned lateral heterojunction bipolar transistor

ABSTRACT

A lateral heterojunction bipolar transistor (HBT) comprising a semiconductor substrate having having a first insulating layer over the semiconductor substrate. A base trench is formed in a first silicon layer over the first insulating layer to form a collector layer over an exposed portion of the semiconductor substrate and an emitter layer over the first insulating layer. A semiconductive layer is formed on the sidewalls of the base trench to form a collector structure in contact with the collector layer and an emitter structure in contact with the emitter layer. A base structure is formed in the base trench. A plurality of connections is formed through an interlevel dielectric layer to the collector layer, the emitter layer, and the base structure. The base structure preferably is a compound semiconductive material of silicon and at least one of silicon-germanium, silicon-germanium-carbon, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a Divisional of application Ser. No. 10/703,284 filed Nov. 6,2003, now U.S. Pat. No. 6,908,824 which is hereby incorporated byreference herein.

BACKGROUND

1. Technical Field

The present invention relates generally to semiconductor technology andmore specifically to lateral heterojunction bipolar transistors andmanufacturing methods therefor.

2. Background Art

A popular device for controllably varying the magnitude of electricalcurrent flowing between two terminals is a three-terminal, a bipolarjunction transistor (BJT). The three terminals include a base terminal,a collector terminal, and an emitter terminal. The movement ofelectrical charge carriers, which produce electrical current flowbetween the collector and the emitter terminals, varies dependent uponvariations in the voltage on the base terminal thereby causing themagnitude of the current to vary. Thus, the voltage across the base andemitter terminals controls the current flow through the emitter andcollector terminals.

The terminals of a BJT are connected to their respective base, collectorand emitter structures formed in a semiconductor substrate. BJTscomprise two p-n junctions placed back-to-back in close proximity toeach other, with one of the regions common to both junctions. There is afirst junction between the base and the emitter, and a second junctionbetween the emitter and the collector. This forms either a p-n-p orn-p-n transistor depending upon the characteristics of thesemiconductive materials used to form the HBT.

Recently, demand for BJTs has increased significantly because thesetransistors are capable of operating at higher speeds and driving morecurrent. These characteristics are important for high-speed,high-frequency communication networks such as those required by cellphones and computers.

BJTs can be used to provide linear voltage and current amplificationbecause small variations of the voltage between the base and emitterterminals, and hence the base current, result in large variations of thecurrent and voltage output at the collector terminal. The transistor canalso be used as a switch in digital logic and power switchingapplications. Such BJTs find application in analog and digital circuitsand integrated circuits at all frequencies from audio to radiofrequency.

Heterojunction bipolar transistors (HBTs) are BJTs where theemitter-base junction is formed from two different semiconductivematerials having similar characteristics. One material used in formingthe base-emitter junction preferably is a compound semiconductivematerial such as silicon (Si) and silicon-germanium (SiGe), orsilicon-germanium-carbon (SiGeC), or a combination thereof. HBTs usingcompound semiconductive materials have risen in popularity due to theirhigh-speed and low electrical noise capabilities, coupled with theability to manufacture them using processing capabilities used in themanufacture of silicon BJTs. Lateral HBTs are HBTs in which the currentflow is parallel to the surface of the substrate on which the HBT ismanufactured. HBTs have found use in higher-frequency applications suchas cell phones, optical fiber, and other high-frequency applicationsrequiring faster switching transistors, such as satellite communicationdevices.

Most BJTs, including HBTs, in use today are “double poly” bipolartransistors, which use two polysilicon structures; one for an emitterstructure, and a second for a base structure of the transistor.

HBTs are manufactured by implanting a silicon substrate with a dopant toprovide a collector region. A silicon layer is then grown or formed overthe collector region. Insulating dividers called shallow-trenchisolations (STIs) are formed in the silicon substrate. The STIs definean intrinsic base region over a portion of the collector region.

Subsequently, a first layer of polysilicon is formed over the siliconsubstrate and is processed to form a base structure in contact with aportion of the intrinsic base region. One portion of the base structureis formed with an opening in which an emitter structure is subsequentlyformed.

A first insulating layer is formed over the base structure and isremoved in the opening of the base structure over the intrinsic baseregion by etching down to the intrinsic base region to form an emitterwindow. The etching process inherently produces a rough surface on thesubstrate since the etchants used are not particularly selective betweenthe polysilicon layer forming the base structure and the underlyingsilicon substrate. To get higher performance, compound semiconductivematerials such as SiGe and SiGeC generally are grown over the insulatinglayer and on the rough surface of the substrate. The rough surfacecauses a major problem because the growth of the compound semiconductivematerial is irregular and its thickness is not constant as a result ofthe roughness of the substrate. This leads to performance problems withthe device and variations in performance from device to device.

A second layer of polysilicon is deposited into the emitter window andprocessed to form an emitter structure, which is encircled by andoverlaps the base structure. The overlap is necessary to provide roomfor an emitter contact, but it causes another major problem withunwanted capacitance between the emitter and base structures. Thiscapacitance slows down the operation of the HBT.

A dielectric layer is formed over the emitter structure and is processedto form spacers around the emitter structure. An interlevel dielectriclayer (ILD) is then formed over the emitter and base structures.

Finally, contacts are formed in the ILD that connect with the collector,base, and emitter structures. Terminals are then connected to thecontacts.

As previously mentioned, the emitter structure overlaps the basestructure because it is necessary to provide room for the emittercontact to be formed. Since it is desirable to make the overlap as smallas possible, it is desirable to have the emitter structure as small aspossible. However, variations in the size of the emitter contact lead toa further major problem causing performance variations in the HBT fromdevice to device.

Although the use of compound semiconductive materials has proven usefulin HBTs, once formed by existing methods, this material is subsequentlysubjected to multiple thermal cycles, implantations and/or etchingprocesses during the formation steps of the remaining elements of theHBT. Such steps include the deposition and etching of oxide layers,nitride layers and subsequently formed polysilicon layers. Several ofthese processing steps inherently damage the compound semiconductivematerial. Etching polysilicon over a compound semiconductive layer, forexample, adversely affects the compound semiconductive material becausethe etchants used do not selectively etch only the polysilicon. Some ofthe compound semiconductive material is also etched during thisprocessing step, resulting in HBTs that are slower and exhibit poornoise performance compared to other HBTs on the same semiconductorwafer.

One attempt to overcome the above-mentioned problems involves selectiveepitaxial growth of the compound semiconductive material only over theactive region of the HBT to form a self-aligned epitaxial intrinsic basestructure. Selective epitaxy also may be used in a self-alignedemitter-to-base process in which an emitter window is defined by growingan in situ doped epitaxial lateral over a patterned thin oxide/nitridepad.

In one method for fabricating a self-aligned double-polysilicon HBTusing selective epitaxy, the intrinsic base is implanted in the siliconsubstrate only in the active region of the silicon substrate. Apolysilicon layer heavily doped with a dopant of a conductivity typeopposite that of the substrate is formed over the active region of thesemiconductor substrate having a given conductivity type.

For example, an n⁻-doped silicon substrate would have p-dopedpolysilicon layers formed thereon. This polysilicon layer then has oneor more compound semiconductive layers epitaxially grown over it. Theselayers are then covered with an upper insulating layer, for examplesilicon dioxide to form a stack above the active region of the HBT. Thepolysilicon layers eventually form the extrinsic base structure of theHBT. The stack is then etched to define an emitter window. Electricallyinsulating regions or “reverse spacers” are separately made on thesidewalls of the emitter window. Next, polysilicon is formed in theemitter window to form the emitter structure. The emitter structure isthus insulated from the extrinsic base structure by the reverse spacersand by a portion of the upper insulating layer of the stack on which theemitter structure partially rests. This results in a more consistentlysmall-sized emitter structure.

The adverse effects of etching the emitter window persist however.During the operation of etching the stack, over-etching still occurs.The lack of adequate controls and reproducibility of over-etchingtypically results in the intrinsic base being implanted after formationof the emitter window. Implantation on the over-etched surface does notovercome the problems associated with the over-etched surface.

Furthermore, to improve the operating speed of a HBT, it is importantthat the base structure be thin enough to minimize the time it takeselectronic charges to move from the emitter to the collector, therebyminimizing the response time of the HBT. It is also important, however,that the base structure have a high concentration of dopant in order tominimize base resistance. Typically, ion implantation techniques areused to form a base layer. However, this technique has the problem ofion channeling, which limits the minimum thickness of the base layer.Another disadvantage of ion implantation is that the compoundsemiconductive layer is often damaged by the ions during implantation.

Additionally, high-temperature annealing typically is required to drivedopants into the various material layers. This annealing step, however,alters the profile of concentration levels of the dopants within thevarious layers of semiconductive materials forming the transistor tocreate undesirable dopant profiles within the various material layers.

Existing methods of manufacturing HBTs still have the problemsassociated with over-etching, the detrimental effects of ionimplantation and annealing, and consistency of manufacturability.

Additionally, existing methods of manufacturing HBTs require deep trenchisolations and buried layers in the substrate. Deep trench isolationsand buried layers use complicated and expensive processing techniques tomanufacture.

Solutions to these problems have been long sought but prior developmentshave not taught or suggested any acceptable solutions and, thus,solutions to these problems have long eluded those skilled in the art.

DISCLOSURE OF THE INVENTION

The present invention provides a lateral heterojunction bipolartransistor (HBT), comprising a semiconductor substrate. An insulatinglayer is formed over the semiconductor substrate. A window is formed inthe insulating layer exposing a portion of the semiconductor substrate,and a silicon layer is formed over the insulating layer and the windowto form a collector layer over the exposed portion of the semiconductorsubstrate and an emitter layer over the insulating layer. A base trenchis etched in the silicon layer over the insulating layer. A siliconspacer is provided on the sidewalls of the base trench to form acollector structure in contact with the collector layer and an emitterstructure in contact with the emitter layer. A base structure of acompound semiconductive material is formed in the base trench.Connections are provided through an interlevel dielectric layer to thecollector layer, emitter layer, and base structure. The base structurepreferably is a material of silicon and at least one ofsilicon-germanium, silicon-germanium-carbon, and combinations thereof.

Certain embodiments of the present invention have other advantages inaddition to or in place of those mentioned above. The advantages willbecome apparent to those skilled in the art from a reading of thefollowing detailed description when taken with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral HBT having a first and a second insulating layer inan interim stage of manufacture in accordance with the presentinvention;

FIG. 2 is the structure of FIG. 1 after removal of the second insulatinglayer;

FIG. 3 is the structure of FIG. 2 after formation of a window in thefirst insulating layer;

FIG. 4 is the structure of FIG. 3 after formation of an epitaxialsilicon layer;

FIG. 5 is the structure of FIG. 4 after formation of a third insulatinglayer;

FIG. 6 is the structure of FIG. 5 after formation of a base trench;

FIG. 7 is the structure of FIG. 6 after formation of a collectorstructure and an emitter structure;

FIG. 8 is the structure of FIG. 7 after formation of a base structure;

FIG. 9 is the structure of FIG. 8 after formation of an interleveldielectric layer;

FIG. 10 is the structure of FIG. 9 after formation of a number ofcontacts;

FIG. 11 is an alternate embodiment of the present invention in aninterim stage of manufacture;

FIG. 12 is the structure of FIG. 11 after patterning an insulatinglayer;

FIG. 13 is the structure of FIG. 12 after formation of a base trench;

FIG. 14 is the structure of FIG. 13 after formation of a collectorstructure and an emitter structure;

FIG. 15 is the structure of FIG. 14 after filling the base trench with acompound semiconductive material;

FIG. 16 is the structure of FIG. 15 after formation of a base connectorlayer;

FIG. 17 is the structure of FIG. 16 after patterning the base contactlayer;

FIG. 18 is the structure of FIG. 17 after formation of a base structure;

FIG. 19 is the structure of FIG. 18 after formation of an insulatingspacer around the base structure;

FIG. 20 is the structure of FIG. 20 after formation of contacts in aninterlevel dielectric layer; and

FIG. 21 is a flow chart of the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are given toprovide a thorough understanding of the invention. However, it will beapparent to one skilled in the art that the invention may be practicedwithout these specific details. In order to avoid obscuring the presentinvention, some well-known system configurations, and process steps arenot disclosed in detail.

Likewise, the drawings showing embodiments of the apparatus aresemi-diagrammatic and not to scale and, particularly, some of thedimensions are for the clarity of presentation and are shown greatlyexaggerated in the FIGs. Generally, the device can be operated in anyorientation.

The term “horizontal” as used in herein is defined as a plane parallelto the conventional plane or surface of a wafer or substrate, regardlessof its orientation. The term “vertical” refers to a directionperpendicular to the horizontal as just defined. Terms, such as “on”,“above”, “below”, “side” (as in “sidewall”), “higher”, “lower”, “over”,and “under”, are defined with respect to the horizontal plane. The term“beside” refers to two structures, which are side by side with neitheroverlapping the other.

The term “processing”, or “processed” as used herein includes depositionof material or photoresist, patterning, exposure, development, etching,cleaning, and/or removal of the material or photoresist as required informing a described structure.

The term “conductivity type” as used herein refers to a semiconductivematerial that uses either electrons as the primary carrier of electricalcharge, on one hand, or holes as the primary carrier of electricalcharge, on the other hand.

Referring now to FIG. 1, therein is shown a lateral HBT 100 in aninterim stage of manufacture in accordance with the present invention.The lateral HBT 100 includes a semiconductor substrate 102, such as alightly doped semiconductive material of a first conductivity type, suchas p⁻ doped silicon. A first insulating layer 106, such as an oxidelayer, is formed over the semiconductor substrate 102.

A second insulating layer 108, such as a nitride layer of a siliconnitride (SiN) compound, is formed over the first insulating layer 106. Anumber of shallow trench isolations (STIs) 112 are formed in thesemiconductor substrate 102. Trenches are formed through the firstinsulating layer 106 and the second insulating layer 108 into thesemiconductor substrate 102. The trenches then are filled with aninsulating material, such as an oxide, to form the number of shallowtrench isolations (STIs) 112. The upper surface is then processed usinga chemical mechanical polish (CMP) process which stops on the secondinsulating layer 108 so that the upper surfaces of the number of STIs112 are coplanar with the upper surface of the second insulating layer108.

Referring now to FIG. 2, therein is shown the structure of FIG. 1wherein the second insulating layer 108 has been removed. The secondinsulating layer 108 shown in FIG. 1 has been removed, for example, byan etching process that stops on the first insulating layer 106 so thenumber of STIs 112 are elevated above the first insulating layer 106.For example, if the first insulating layer 106 is an oxide layer and thesecond insulating layer 108 is a nitride layer, an etchant is used whichselectively etches only the nitride layer leaving the oxide layerunetched.

Referring now to FIG. 3, therein is shown the structure of FIG. 2 afterformation of a window 300 in the first insulating layer 106. The window300 is formed, for example, by using photolithographic processes todefine an area of the first insulating layer 106 over a portion of thesemiconductor substrate 102, and then etching that area of the firstinsulating layer 106 to form the window 300 over a portion of thesemiconductor substrate 102.

Referring now to FIG. 4, therein is shown the structure of FIG. 3 afterformation of a first silicon layer 400, such as a heavily dopedsemiconductive material of the second conductivity type, such as n+doped silicon. The first silicon layer 400 may be either epitaxiallygrown or formed by means of a chemical vapor deposition (CVD), and thenprocessed further using CMP so the upper surface of the first siliconlayer 400 is coplanar with the upper surfaces of the number of STIs 112.The first silicon layer 400 will be monocrystaline silicon in the areaof the window 300 and polysilicon in the area over the first insulatinglayer 106.

Referring now to FIG. 5, therein is shown the structure of FIG. 4 afterformation of a third insulating layer 500, such as an oxide layer. Thethird insulating layer 500 is formed or grown over the first epitaxialsilicon layer 400. A photoresist layer 502 is deposited and patterned tocreate a base trench mask 504.

Referring now to FIG. 6, therein is shown the structure of FIG. 5 afterformation of a base trench 600. The third insulating layer 500 and thefirst silicon layer 400 are etched down to the first insulating layer106 using the base trench mask 504 shown in FIG. 5. This exposes thenumber of STIs 112 and the first insulating layer 106. Moreparticularly, the etching forms the base trench 600. The base trench 600separates the combination of the third insulating layer 500 and thefirst silicon layer 400 into two portions. The portion of the firstsilicon layer 400 shown in FIG. 5 in contact with the semiconductorsubstrate 102 forms a collector layer 602. The portion of the firstsilicon layer 400 shown in FIG. 5 over the first insulating layer 106forms an emitter layer 604. The base trench mask 504 is then removed.

Referring now to FIG. 7, therein is shown the structure of FIG. 6 afterforming a collector structure 700 laterally on the collector layer 602and an emitter structure 702 laterally on the emitter layer 604. Thecollector structure 700 and the emitter structure 702 preferably areformed by selective epitaxial growth of a second silicon layer, such asa lightly doped semiconductive material of the second conductivity type,such as n⁻ doped silicon. The second silicon layer can be lightlypredoped during formation of the second silicon layer. The secondsilicon layer is formed only on the sidewalls of the base trench 600 andnot on the first insulating layer 106 or the third insulating layer 500,thus forming the collector structure 700 and the emitter structure 702on the sidewalls of the base trench 600.

Alternatively, formation of the collector structure 700 and the emitterstructure 702 can be avoided by forming the collector layer 602 and theemitter layer 604 by selective epitaxy. The collector layer 602 and theemitter layer 604 can be selectively grown in their respective regions.The collector layer 602 can be selectively grown over the semiconductorsubstrate 102, and the emitter layer 604 can be selectively depositedover the first insulating layer 106.

Referring now to FIG. 8, therein is shown the structure of FIG. 7 afterdeposition and processing of a compound semiconductive layer to form abase structure 800 entirely on the first insulating layer 106 over thecollector structure 700 and the emitter structure 702 in the base trench600. The compound semiconductive layer forming the base structure 800preferably is silicon (Si) and at least one of silicon germanium (SiGe),silicon germanium carbon (SiGeC), and combinations thereof. The basestructure 800 fills the base trench 600 shown in FIG. 6 and FIG. 7 andis processed so the top surface of the base structure 800 issubstantially coplanar with the top surface of the third insulatinglayer 500.

Referring now to FIG. 9, therein is shown the structure of FIG. 8 afterformation of an interlevel dielectric (ILD) layer 900, such as an oxidelayer, which is planarized using a CMP process.

Referring now to FIG. 10, therein is shown the structure of FIG. 9 afterformation of the contacts of the lateral HBT 100. The lateral HBT 100has a collector contact 1002, a base contact 1004, and an emittercontact 1006 formed in the ILD layer 900. The collector contact 1002 isformed by providing a hole through the ILD layer 900 and the thirdinsulating layer 500 into the collector layer 602. The base contact 1004is formed by providing a hole through the ILD layer 900 into the basestructure 800. The emitter contact 1006 is formed by providing a holethrough the ILD layer 900, and the third insulating layer 500 into theemitter layer 604. The collector contact 1002, the base contact 1004,and the emitter contact 1006 comprise a conductive material, such astungsten (W) formed into the trenches.

Referring now to FIG. 11, therein is shown an alternate embodiment ofthe present invention in an interim stage of manufacture using asilicon-on-insulator (SOI) wafer. A lateral HBT 1100 includes asemiconductor substrate 1102, such as a lightly doped semiconductivematerial of a first conductivity type, such as p⁻ doped silicon, thathas an insulating layer 1104, such as an oxide layer, on the topthereof. A first silicon layer 1106, such as a heavily dopedsemiconductive material of a second conductivity type, such as n⁺ dopedsilicon, is then formed on the insulating layer 1104.

A number of STI's 1108 is formed in the first silicon layer 1106 in aconventional manner. A second insulating layer 1110, such as an oxidelayer, is then formed over the number of STIs 1108 and the first siliconlayer 1106. A CMP is performed to planarize the upper surface of thesecond insulating layer 1110.

Referring now to FIG. 12, therein is shown the structure of FIG. 11wherein a photoresist layer 1200 has been deposited and patterned toform a base trench mask 1202 over the second insulating layer 1110.

Referring now to FIG. 13, therein is shown the structure of FIG. 12after formation of a base trench 1300. The base trench 1300 is formed byetching the second insulating layer 1110 and the first silicon layer1106 of FIG. 12 using the base trench mask 1202 of FIG. 12. The basetrench 1300 separates the combination of the second insulating layer1110 and the first silicon layer 1106 of FIG. 12 into two portions.

In this embodiment, the two portions are the same so either can be thecollector portion or the emitter portion. For convenience ofterminology, the portion of the first silicon layer 1106 on the left ofFIG. 13 is designated as a collector layer 1302 and the portion of thefirst silicon layer 1106 on the right of FIG. 13 is designated as anemitter layer 1304. The photoresist layer 1200 shown in FIG. 12 is thenremoved leaving the remainder of the two portions of the secondinsulating layer 1110 on the upper surface of the structure.

Referring now to FIG. 14, therein is shown the structure of FIG. 13after formation of a collector structure 1400 laterally on the collectorlayer 1302 and an emitter structure 1402 laterally on the emitter layer1304. The collector structure 1400 and the emitter structure 1402 areformed by selective epitaxial growth of a lightly doped semiconductivematerial of the second conductivity type, such as an n⁻ doped silicon.

Referring now to FIG. 15, therein is shown the structure of FIG. 14after the base trench 1300 is filled with a compound semiconductivelayer 1500 entirely on the insulating layer 1104. The compoundsemiconductive layer 1500 preferably comprises silicon (Si) and at leastone of silicon-germanium (SiGe), silicon-germanium-carbon (SiGeC), andcombinations thereof.

Referring now to FIG. 16, therein is shown the structure of FIG. 15after deposition of a base connector layer 1600 and a third insulatinglayer 1602. The base connector layer 1600 is formed over the compoundsemiconductive layer 1500 used to fill the base trench 1300, such as bydepositing a layer of a heavily doped semiconductive material of thefirst conductivity type, such as p⁺ doped polysilicon. The thirdinsulating layer 1602, such as a nitride layer, is then formed over thebase connector layer 1600.

Referring now to FIG. 17, therein is shown the structure of FIG. 16after a photoresist layer 1700 has been deposited and processed. Thephotoresist layer 1700 defines an area over the base trench 1300 shownin FIG. 14, which has been filled by the collector structure 1400, theemitter structure 1402, and the compound semiconductive layer 1500.

Referring now to FIG. 18, therein is shown the structure of FIG. 17after formation of a base structure 1800. The third insulating layer1602, the base connector layer 1600, and the compound semiconductivelayer 1500, all shown in FIG. 17, are etched using the photoresist layer1700 of FIG. 17. The base structure 1800 comprises a base layer 1804formed from the compound semiconductive layer 1500 and a base connector1806 formed from the base connector layer 1600. An insulating cap 1808is formed over the base structure 1800 from the third insulating layer1602.

Referring now to FIG. 19, therein is shown the structure of FIG. 18after formation of an insulating spacer 1900, such as a nitride spacer.The insulating spacer 1900 is formed around the base structure 1800,such as by depositing a layer of insulating material, such as nitride,and then etching the layer of insulating material to form the insulatingspacer 1900.

Referring now to FIG. 20, therein is shown the structure of FIG. 19after formation of the various contacts for the lateral HBT 1100. Thecontacts are formed by providing an ILD layer 2000, which is formed forexample, by depositing an insulating material, such as oxide, and thenperforming a CMP process to planarize the upper surface of the ILD layer2000. The ILD layer 2000 is then processed to form holes that are filledwith a conductive material, such as tungsten (W), to provide the variouscontacts of the lateral HBT 1100.

A collector contact 2002 is formed by filling a hole through the ILDlayer 2000 that comes into contact with the collector layer 1302. A basecontact 2004 is formed by filling a hole through the ILD layer 2000 andthe insulating cap 1808 to the base structure 1800. An emitter contact2006 is formed by filling a hole through the ILD layer 2000 into contactwith the emitter layer 1304. The collector contact 2002 and the emittercontact 2006 are on opposite sides of the base structure 1800. Theinsulating cap 1808 and the insulating spacer 1900 are used in thisdevice to enable use of standard self-aligned contact processingtechniques thereby further reducing the size of the lateral HBT 1100.

Referring now to FIG. 21 therein is shown a flow diagram of a method2100 of the present invention. The method 2100 comprises a block 2102 ofproviding a semiconductor substrate; a block 2104 of forming a firstinsulating layer over the semiconductor substrate; a block 2106 offorming a first silicon layer over the first insulating layer; a block2108 of forming a base trench in the first silicon layer to form anemitter layer and a collector layer; a block 2110 of providing asemiconductive layer on the sidewalls of the base trench to form anemitter structure in contact with the emitter layer and a collectorstructure in contact with the collector layer; a block 2112 of forming abase structure of a compound semiconductive material in the base trench;a block 2114 of forming an interlevel dielectric layer; and a block 2116of providing a plurality of connections through the interleveldielectric layer to the emitter layer, collector layer, and basestructure.

While the invention has been described in conjunction with specific bestmodes, it is to be understood that many alternatives, modifications, andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications, and variations, which fall within thespirit and scope of the included claims. All matters set forth herein orshown in the accompanying drawings are to be interpreted in anillustrative and non-limiting sense.

1. A lateral heterojunction bipolar transistor comprising: asemiconductor substrate; a first insulating layer over the semiconductorsubstrate; a first silicon layer over the first insulating layer; a basetrench in the first silicon layer to form an emitter layer and acollector layer; a semiconductive layer on the sidewalls of the basetrench to form a collector structure in contact with the collector layerand an emitter structure in contact with the emitter layer; a basestructure of a compound semiconductive material in the base trenchentirely on the first insulating layer; an interlevel dielectric layer;and a plurality of connections through the interlevel dielectric layerto the collector layer, the emitter layer, and the base structure. 2.The lateral heterojunction bipolar transistor as claimed in claim 1wherein the base structure comprises a compound semiconductive materialof silicon and at least one of silicon-germanium,silicon-germanium-carbon, and combinations thereof.
 3. The lateralheterojunction bipolar transistor as claimed in claim 1 wherein: thesemiconductor substrate comprises a lightly doped semiconductivematerial of a first conductivity type; the first silicon layer comprisesa heavily doped semiconductive material of the second conductivity type;and the semiconductive layer on the sidewalls of the base trenchcomprises a lightly doped semiconductive material of the secondconductivity type.
 4. The lateral heterojunction bipolar transistor asclaimed in claim 1 wherein: the first insulating layer has a window toexpose a portion of the semiconductor substrate; and the base trench inthe first silicon layer forms a collector layer over the exposed portionof the semiconductor substrate and an emitter layer over the firstinsulating layer.
 5. The lateral heterojunction bipolar transistor asclaimed in claim 4 wherein the base structure comprises a compoundsemiconductive material of silicon and at least one ofsilicon-germanium, silicon-germanium-carbon, and combinations thereof.6. A lateral heterojunction bipolar transistor comprising: asemiconductor substrate of a first conductivity type; a first insulatinglayer over the semiconductor substrate; a first silicon layer of asecond conductivity type over the first insulating layer; a base trenchin the first silicon layer to form a collector layer and an emitterlayer; a silicon spacer of the second conductivity type on the sidewallsof the base trench to form a collector structure in contact with thecollector layer and an emitter structure in contact with the emitterlayer; a base structure of a compound semiconductive material in thebase trench entirely on the first insulating layer; an interleveldielectric layer; and a plurality of connections through the interleveldielectric layer to the collector layer, the emitter layer, and the basestructure.
 7. The lateral heterojunction bipolar transistor as claimedin claim 6 wherein the base structure comprises a compoundsemiconductive material of silicon and at least one ofsilicon-germanium, silicon-germanium-carbon, and combinations thereof.8. The lateral heterojunction bipolar transistor as claimed in claim 6wherein: the first silicon layer comprises a heavily dopedsemiconductive material of the second conductivity type; and thesemiconductive layer on the sidewalls of the base trench comprises alightly doped semiconductive material of the second conductivity type.9. The lateral heterojunction bipolar transistor as claimed in claim 6wherein: the first insulating layer has a window to expose a portion ofthe semiconductor substrate; and the base trench in the first siliconlayer forms a collector layer over the exposed portion of thesemiconductor substrate and an emitter layer over the first insulatinglayer.
 10. The lateral heterojunction bipolar transistor as claimed inclaim 9 wherein the base structure comprises a compound semiconductivematerial of silicon and at least one of silicon-germanium,silicon-germanium-carbon, and combinations thereof.